Chromatography system with tilt-prevention structure and associated process

ABSTRACT

Chromatography apparatus and methods are described, especially for expanded bed adsorption. A column tube has a process fluid input device at the bottom and a movable piston in the top. The piston is enclosed in the column by a cover plate. The piston body has an inflatable seal, and is connected by a frame to a contact ring which carries another inflatable member to contact the tube wall. Process fluid leaves the operating volume through an opening of the piston and flexible hose, through the enclosed space and out through the cover plate. The space above the piston can be pressurised to control piston movement. The contact ring maintains piston alignment. The inflatable seals are used to fix the piston in position, allow it to slide or allow washing. The piston outlet may include a vortex-inhibitor. Bed and piston levels may be monitored by ultrasound sensors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/GB2014/050456 filed Feb. 17,2014, which claims priority to GB1302714.9 filed Feb. 15, 2013, both ofwhich are hereby incorporated by reference.

BACKGROUND

This invention has to do with apparatus, systems and processes forchromatography. Aspects of the invention have particular relevance forexpanded bed (fluidised bed) processes. These are processes in which aprocess liquid is contacted with a bed of solid particulate medium in acolumn, by passing the liquid through the column. Contact with the solidmedium allows treatment of the liquid, in most cases the treatmentconstituting or comprising separation of a component of the processliquid by retention thereof on the medium.

Chromatography has traditionally used packed beds of particulate medium,retained between end retaining structures of the column tube which keepthe bed of medium in place while allowing passage of the liquidcomponents. The end retaining structures (sometimes called “cells”) havea mesh through which liquid but not media particles can pass. The cellsmay be fixed to the column tube, or one or both of them may beoperationally slidable within it, with a piston seal, for adjustment ofbed height.

In recent years the industrial-scale production of biologically-producedmolecules, e.g. for drugs, vaccines or diagnostic agents, has become ofgreat technical and economic importance. Many such products are producedin cell cultures and they (or their precursors) must be separated from aculture product (e.g. homogenised broth or slurry) which typicallycontains insoluble solids such as cell debris as well as contaminants;it cannot be passed as mobile phase through a packed bed to adsorb theproduct chromatographically (preparative chromatography) because thesolids would block the system. Rather, the culture product must first beprocessed to remove the solid matter and make a process liquid able topass through stationary phase beds.

Expanded Bed Adsorption (EBA) enables separation of target componentsfrom such process liquids without preliminary centrifugation orfiltration. In EBA the process liquid runs up through a bed of adsorbentmedium particles in expanded (fluidised) state. Solid material in theprocess liquid passes up right through the bed to the outlet; the inletand outlet are without meshes. Target product is adsorbed onto theparticulate medium and is subsequently eluted (washed) from it, eitherdownwardly with the bed packed or upwardly with the bed fluidised.

EBA therefore offers important efficiencies. For example, because it candirectly process liquids containing high proportions of solids or oftarget substance, such as high cell density broths from a bioreactor, itenables the high productivity of such bioreactor processes to be carriedthrough the later processing.

However EBA also presents major technical challenges. It is difficult tomaintain the expanded bed in a stable and effective state, e.g.maintaining the vertical gradation of reducing particle size, andavoiding direct channeling of process liquid through the bed.

Measures taken to control bed behaviour include special process liquidinjection arrangements at the bottom of the column, to produce plug-likeflow e.g. by injecting the liquid through an array of holes distributedover the bottom cell, optionally stirring with a rotating stirrer. Or,an array of process liquid injection holes is in a motor-drivendistribution rotor. At the top of the bed a movable piston or float maylie on the liquid surface to mount the process liquid outlet, or theoutlet tube may simply dip into the clear liquid (“headspace” orsupernatant) above the particle bed.

EBA columns are relatively tall, because of the bed expansion. Expandedbed height—which may be about twice the rest height—is controlled byadjustment of the liquid flow rate, optionally in conjunction with a toppiston or float as mentioned. Top pistons are problematic because themounting and control structure connecting them through the end of thecolumn (usually a pipe incorporating the outlet conduit and/or guiderods) needs large vertical clearance.

Solids passing through the column may accumulate and foul theapparatus—cell materials are often sticky—which is then difficult todisassemble for cleaning. As the apparatus is scaled up, bed diameterincreases, components become larger and heavier and serious operationaldifficulties may arise.

As a consequence of these various technical challenges, scale-up of EBAfor industrial application has scarcely progressed despite the intrinsicmerits of the EBA method in itself.

SUMMARY

We propose new kinds of chromatography apparatus and chromatographyprocesses with a view to enhancing and facilitating the operation ofapparatus and processes of the kind described, especially but notexclusively EBA. One particular aspect addressed is construction,operation and control of a movable end cell or piston.

Particular advantages are envisaged for scale-up of EBA and also othermovable-cell apparatus and methods

General Context

The apparatus aspects of the invention relate in general tochromatography apparatus comprising a column tube and first and secondend retainer structures (end cells) which close off the column tube atrespective axially-spaced first and second positions to define betweenthem an operating volume which in use contains a stationary phasematerial, typically a bed of particles. The apparatus has first andsecond process fluid conduits communicating into the operating volume atthe first and second positions, preferably through the end cells, forliquid e.g process fluid or mobile phase liquid such as buffer(equilibration, elution, wash) to enter and leave the operating volumein use.

Movable Piston Proposals

In a first aspect, at least one of the end cells is a movable piston,slidably axially movable inside the tube over a range of operationalpositions and comprising a peripheral fluid-tight operating seal whichseals against the inside of the column tube in operation to prevent thepassage of liquid. It may be the top cell of an upright column.

One proposal in this aspect is that the piston comprises a piston body,which mounts or comprises the operating seal and closes off the tube(except for any said process fluid conduit therein, which is desirablypresent, preferably at the centre) and additionally a tilt-preventionstructure, connected to and rigidly axially-aligned with the pistonbody, the tilt-prevention structure having acircumferentially-distributed contact structure which engages around theinterior of the column tube at an axial spacing from the operating sealto maintain axial alignment of the piston in the column tube. Thecontact structure may slide against the tube interior surface.

Preferred features of the piston are as follows, which (insofar as theyare compatible) are desirably combined.

The contact structure may be annular and engage continuously around thetube interior. If however it has plural circumferentially-spaced contactelements these are preferably spaced by angular circumferential gaps notmore than 90°, preferably not more than 70°, more preferably not morethan 45° or not more than 30°, to assure adequate tilt-prevention. Itmay be non-metallic, e.g. polymeric or elastomeric. It may be anelastomeric ring, although it does not have a sealing function. Thecontact structure may be radially movable in the tilt-preventionstructure and the piston may comprise a contact structure actuatingmechanism such as a pneumatically-actuated mechanism for urging thecontact structure radially outwardly against the tube interior and/orfor retracting it to a radially retracted condition or position. Apreferred contact structure is or comprises an elastomeric ring, e.g. ahollow ring, with a pneumatically-actuated mechanism for urging itoutwards. A pneumatic gas line may connect between this mechanism andthe exterior of the apparatus, e.g. out through an end of the tube, suchas through an end plate or cover.

Desirably the contact structure of the tilt-prevention structure and theoperating seal are the only piston parts engaging the column, so thatthe piston can travel along the column without tilting or jamming,without having a rigid connection (such as the axial piston rod pipes orguide rods of the prior art) engaging (passing) through a fixed columnend structure of the apparatus. That is, the piston may be entirelyinside the column tube, and be self-aligning with the column tube axisby its axially-distributed engagements with the column wall.

The engaged locus of the contact structure may be at a constant axialspacing from the operating seal, around the tube. Preferably it contactsthe tube interior at a single annular locus spaced from the operatingseal (e.g. a circle parallel to that of the seal), contacting eithercontinuously or intermittently around the circle.

Preferably the tilt-prevention (or stabilising) structure does notcontact the column wall between the operating seal and the contactstructure. Desirably the tilt-prevention structure is open, in the sensethat the column wall behind the operating seal, i.e. between theoperating seal and the contact structure, is open or exposed to thecolumn tube interior space behind the piston (i.e. outside the operatingvolume). This can facilitate access and cleaning. Of course in principlehowever tilt-prevention may be provided simply by sufficient axiallength of a piston body.

The tilt-prevention structure may comprise an open frame e.g. comprisingor consisting of rods, legs or struts with intervening spacing. Theframe can connect an annular body supporting the operating seal to thecontact structure, which may itself be, comprise or be mounted on anannular body.

Alternatively, if the contact structure has pluralcircumferentially-spaced contact elements these may be provided onrespective axially projecting legs or struts, e.g. extending from theoutside of the piston body. The piston body is closed, e.g. as a plateor disc, except for any process fluid inlet through it, whereas thecontact structure or support body for it may be an open ring. The back(outer side) of the piston body may be exposed through the contactstructure, so a connector or union comprised in or fixed to the pistonbody, for a fluid conduit, may be exposed and operable on the outer sideof the piston body. The same may be true of one or more otherconnectors, e.g. for actuation of dynamic elements as discussed below.

The degree of axial spacing needed between the tilt-preventing contactstructure (or the axially-extreme part thereof) and the operating sealwill depend on the dimensions of the column, the piston and on thestructure at the operating seal. Axial alignment needs to be maintainedsufficiently to maintain the seal and to prevent jamming of the piston.This may take into account the extent to which the operating sealprojects relative to its surrounding mounting, which may be of a hardmaterial e.g. metal which to avoid damage should not contact the tubeinterior especially if the latter is of plastics material. Typically theaxial extent (the maximum distance reached by the contact structure awayfrom the operating seal axial position) is at least 20%, at least 25% orat least 30% of the diameter of the piston (or of the correspondinginternal diameter of the column tube).

The operating seal of the piston body may be of any suitable kind, forexample an elastomer ring (single or multiple). The piston body may havea peripheral groove or channel in which it is mounted or housed. Amechanism or means may be provided for advancing or retracting theoperating seal radially, e.g. to urge it outwardly against the tubeinterior to enhance the seal at a selected position, and/or to retractit to loosen or release the seal and facilitate or allow movement of thepiston along the tube, or the passage of liquid around it e.g. forcleaning. A pneumatic mechanism is preferred for this radial drive oractuation of the seal, being easily actuated from outside the columntube. A pneumatic gas line for this purpose may connect to the pistonbody and extend through an interior gas space which when pressurisedexpands the operating seal. Depending on the structure, material anddimensions of the seal either of the retraction or the expansionmovement/urge may be under elastic recovery or under forced actuation bya mechanism as mentioned. The seal may be radially retractablesufficiently to form an annular clearance between the seal and thecolumn tube wall. For process purposes, this clearance is desirablylarger than the largest media particles used in the column. When engagedwith the tube wall, e.g. under radially outward actuation as proposed,the operating seal may function to grip the tube to hold the piston inposition e.g. against its own weight and/or against positive fluidpressure from above or below. Or, the contact structure or a combinationof the contact structure and seal may serve this function.

The piston body desirably has a central opening as (or for) the processfluid/mobile phase conduit. This opening may receive or form a union orconnector, for connecting to a flexible process fluid/mobile phaseconduit outside the piston body. A conventional releasable liquid-tightconnector such as a triclamp is suitable. Preferably the inner face ofthe piston body, directed onto to the operating volume, is convergenttowards the conduit entrance, to facilitate smooth flow and escape ofliquid and gas through the opening. If it is an expanded bed apparatus,this inner face may be directly exposed to the operating volume. If itis a packed bed, there may be an overlying mesh layer to prevent thepassage of particles. The form of a converging inner surface may beconical or dished. If conical, the cone angle relative to the radialplane is preferably between 4° and 25°.

The materials used for the piston and tilt-prevention structure thereofwill depend on the size of the apparatus and the chosen structure, buttypically metal and/or engineering plastic materials are suitable. Thepiston is preferred not to be a buoyant or floatable component. Steel isgenerally good, but heavy and expensive. Engineering plastics such asPEEK are very good but expensive. Large shaped components subject toprimarily general pressures and stresses, such as a piston body, may bemade from standard plastics such as polypropylene which are muchcheaper, easier to form and have adequate strength.

A second proposal concerning the moveable piston, which may have any ofthe features proposed above in the first proposal, is apparatus andmethods providing for the use of pressurised gas in a pneumatic spacebehind (outside) the movable piston to control the piston's position,i.e. to hold or change its axial position in the column tube. For thispurpose, apparatus has a gas-tight pneumatic space defined outside themovable piston, preferably by the column tube and an outer closure (e.g.an end plate) thereof. Means are provided for supplying pressurised gasinto this pneumatic space to act on the movable piston, e.g. directly onthe outer surface of the piston body of a self-aligning piston asdescribed in the first proposal above. A gas supply line may connectinto the pneumatic space through the column tube wall or, morepreferably, through an end plate constituting the outer closure andwhich can be removed from the column tube. A gas supply is connected tothe gas supply line. A gas pressure control for the gas supply line canbe provided, preferably as part of the apparatus (i.e. as distinct froma control on the supply itself), and desirably provide both a shut-offcondition and a range of maintainable operating pressures. The operatingpressures need not be high for most processes, e.g. in a range of 0 to 5bar (gauge pressure). However higher pressures e.g. up to 10 barg may beused if supported by the apparatus. The gas supply may be sterile or viaa sterilising filter in the supply line, enabling sterile conditions inthe space outside the piston during operation.

Usually, at various stages of a chromatography process, the operatingvolume is at raised pressure and this must be contained by the end cells(i.e. retaining structures or closures). Where a movable piston providesan end cell, the structure and material of the piston and the means bywhich the piston is held and moved must all be able to withstand thisbed pressure or operating fluid pressure, which for large columns meansheavy and awkward components. By applying pneumatic pressure on theoutside of a movable piston to counter-balance all or part of the liquidpressure on the other side, the strength demands on the piston arereduced and it can be made lighter and easier to handle.

Thus it can be arranged that the piston and its components (includingthe operating seal) may need to withstand only the difference betweenthe pressures in the pneumatic space and the operating volume, both ofwhich pressures are controllable, together with any frictionalresistance during position change, the weight of the piston itself andthe structural forces involved in alignment via the contact structureand in urging the seal and contact structure out against the tube wall.The difference in pressures is usually/typically less than 0.5 bar, andmay be controlled or controllable to such low differential pressures,e.g. less than 0.5 bar in an EBA process. The general balancing of axialforces also facilitates the radial actions/movements of the piston withoperating seal and contact structure.

Where the piston engages the piston wall by means of an inflatableelement e.g. a seal, and the column interior is pressurised, it isnecessary to provide adequate excess inflation pressure to enable theinflatable element to expand against the surrounding pressure in thecolumn.

The fluid pressure in the operating volume may be sufficient to move themovable piston outwardly (usually upwardly). So, both inward and outwardpiston movements may be available by adjustment of the gas pressure(e.g. air pressure) in the pneumatic space, without necessarily needingto adjust the liquid flow pressure in the operating volume as well,although of course that is also a possibility but usually the processfluid flow is adjusted primarily or only with the bed behaviour in mind.In some other kinds of chromatography processes the piston may beallowed to move to accommodate volume changes of a packed media bed,e.g. swelling or shrinking of the medium as the ionic composition of thesurrounding liquid changes.

One particular desirable context for such apparatus and procedures isexpanded bed or fluidised bed chromatography, in which the movablepiston is the top cell of an upright column. A central process fluidoutlet of the movable piston may connect to the exterior of the columnvia a flexible conduit e.g. a polymeric hose, which may extend throughthe pneumatic space and through the column tube (or an end closurethereof) via a sealed isolated connector to maintain the gas-tightcondition of the space. The flexible conduit can flex or contract/extendto accommodate the necessary operational range of axial movement of thepiston and so that it can fit in the pneumatic chamber at less than fullextension.

An expanded bed or fluidized bed chromatography process, or separationor purification process, in which the height of the movable piston isadjusted by controlling gas pressure in the pneumatic space, is anaspect of the present proposal. Most preferably it uses a self-aligningpiston as described in the first aspect above. Thus, unlike the proposalin U.S. Pat. No. 5,366,621 to use gas pressure behind a piston to helpmove the piston, this proposal would then not involve rigid pistonsupport structures extending out through the end of the column. Thepiston can therefore be both lighter in weight and vertically compact,and correspondingly better suited for scaling-up. Thus, while columndimensions are not especially critical for operational effectiveness, weenvisage greatest benefit in application of our proposals in largerpreparative-scale apparatus e.g. column diameters of at least 100 mm, orat least 200 mm, or preferably at least 300 mm for expanded fluidisedbed apparatus and processes, or at least 750 mm or at least 1000 mm indiameter for packed bed apparatus and processes (including ion-exchange)which may be as large as e.g. 4 m diameter, although these too may besmaller e.g. down to 300 or 100 mm diameter and still have advantages.Column height is important insofar as conventional larger columns haveused long piston guides which, with a stand, greatly increased heighte.g. so that a 1 m column tube has needed more than 2 m availableoperating height.

Nevertheless the principles described are also effective with smallercolumns, e.g. laboratory-scale columns such as from 5 to 50 mm diameter,and columns less than 1 m long (high).

The column tube may be of any suitable material, e.g. conventionalmaterials such as transparent plastics (e.g. acrylic) or metal e.g.steel. Transparent column tubes are preferred in some processes forvisual monitoring. In expanded/fluidised bed apparatus a transparenttube is preferred.

In packed bed apparatus and processes, the need to move a top pistonthrough large distances can be less than in expanded bed processes.However there will be a need for substantial movement, because the bedis usually packed from slurry filled into the column, and the distancemoved by the piston to the packed condition will correspond to thedilution % of the slurry. With some packed processes (such as ionexchange) there may be significant expansion or contraction of the bedduring processing. The pistons may be very large and cumbersome. Thepresent proposals for the use of pneumatic pressure-balancing drive witha self-aligning piston are valuable, therefore. Conventional largecolumns with top pistons often use a set of hydraulic rams positionedaround or above the column tube to support and move the piston. Theseare bulky structures, and control of the rams so that they act togetherto slide the piston without tilting and jamming is difficult andrequires sophisticated apparatus. By deploying gas pressure in anenclosed pneumatic space behind the piston, as proposed herein, thepiston can be made lighter in structure and more easily handleable andcontrollable. A set of hydraulic rams can be omitted.

A third aspect of our proposals relating to movable pistons is about theaxial positioning and control of the movable piston in the column tube.

In combination with either or both of the previous proposals about thestructure and control of the movable piston, we prefer that theapparatus comprises sensing means for detecting the axial position inthe column tube of the movable piston and/or of features of a mediaparticle bed or particle distribution (especially in the context of EBAin which there is usually a liquid-filled headspace or supernatant,which in turn may have a clear upper part and a cloudy/turbid lowerpart, between the top of the bed and the underside of the piston).Firstly, such sensing means may determine and may also indicate anyoperational position taken by the piston in the tube. Additionally oralternatively, a sensing means may comprise means for determiningwhether the axial position of the piston registers with one or morepredetermined axial positions relative to the column, e.g. apredetermined lower position (perhaps corresponding to a packed bedstate, e.g. for eluting an EBA column) and a predetermined upperposition (e.g. corresponding to a predetermined adsorption stageposition of an expanded bed column with the bed expanded, a stableexpanded bed height position with a predetermined height of supernatante.g. clear supernatant, or corresponding to a position for cleaning orservicing the apparatus). For that purpose, position-specific sensingmeans may be provided mounted at the side of the column tube at thecorresponding positions, and able to detect the presence of the pistonby any means appropriate to the nature of the piston and column tubewall, e.g. optically or by ultrasound.

Secondly, sensing means such as ultrasound may operate/be operable todetect position or condition of features of the medium particles, thebed thereof, or materials passing through or in the bed. Potentiallyuseful detectable and/or measurable features include any one or more ofthe top of a bed (or expanded bed), the position of an interface betweenan expanded bed and clear supernatant, the height of a bed or expandedbed, the height of a supernatant liquid layer, the presence or height ofa cloudy or turbid (low medium concentration) supernatant region orlayer, the presence/position of an interface between cloudy and clearsupernatant regions, the presence/position of an interface between acloudy supernatant region and an expanded bad regions. The packed,expanded, stable or unstable conditions of a bed, regions of clearsupernatant, cloudy regions or regions of lower medium concentration maybe detected, e.g. using density-dependent detection such as ultrasound.Concentrations or concentration variations of other (non-medium)substances in the bed may also be detected, such as solutes of intereste.g. target molecules, or non-medium particles.

In relation to the apparatus and process proposals above for driving themovement of the piston, preferably by pneumatic means, the apparatus maycomprise and the process may use a control system to control the gaspressure in the pneumatic space (to adjust, change or maintain the axialposition of the piston) in dependence on signals received from theposition/condition-sensing means, which in turn depend on the positionof the piston or on the position or condition of or in the particle bedor of the top of the bed, or on the detection of media particles orother particles or substances in general. This control system may enableor provide automated control of the piston position or bed condition(although visual/manual intervention may be used instead oradditionally) in dependence on column or process conditions (of any ofthe detectable kinds set out above) in real time, e.g. as a mode ofProcess Analytical Technology whereby process and product quality aredesigned, analysed or controlled with measurement of critical processparameters.

For monitoring such positions over a range, the apparatus may comprise aset or array of sensors or detectors distributed axially (usuallyvertically) on or at the side of the column tube and acting laterally(e.g. detection path in a radial plane). Additionally or alternativelythe system may have a sensor acting axially (axially-extending detectionpath) which can measure the axial position of the piston e.g. as adistance relative to an end plate or end closure of the column.

Position-specific sensors may be e.g. ultrasound, optical, capacitive orinductive detectors (often with a combination of transmitter andreceiver, preferably combined in a single transceiver) mounted on oradjacent the column tube wall, preferably with axial positionadjustability relative to the column tube. A position-specific detectormay include an indicator that any of the piston, bed front, mediaparticles or clear liquid is present at the predetermined position, onthe detection path. One or more supplementary detectors or sensors maybe provided axially adjacent any mentioned predetermined position toindicate approach, overshoot or undershoot of the correspondingentity/condition to be detected (piston, bed front, liquid, mediaparticles etc. as described above) relative to the predeterminedposition.

In preferred apparatus, desirably for expanded bed or fluidised bedcolumns but not limited to these, piston position detection is by meansof an ultrasound transceiver mounted vertically adjustably, e.g.slidably, adjacent the tube wall, e.g. on a vertical support element ofthe apparatus, and securable at any of a range of axial positions. A setof such transceivers may be used to provide detection of adjacentpositions as mentioned above, e.g. a set of at least two or at leastthree axially adjacent sensors.

Transceiver Mounting

An independent proposal herein is for the mounting of an ultrasoundtransmitter, receiver or transceiver. Ultrasound transducers generallyneed to make close contact at a suitable pressure against the surface ofthe tube to operate effectively. It is desirable, but difficult, toreach this condition by advancing the transducer gradually against thetube surface, to a controlled extent and pressure. To this end, wepropose mounting an ultrasound transducer (e.g. a transceiver) on or ina pivoted mounting element adjacent to the column tube. The transducerface is to one side of the pivot. To the other side of the pivot, themounting element carries a rotatable threaded adjuster element with anend positioned to bear against the column tube wall. The end that bearsagainst the tube wall may be of a plastics material, if necessary, toavoid damage to the tube surface. Turning the adjuster with its endagainst the tube wall controllably and gradually pushes that end of themounting element away from the tube wall, by threaded engagement withthe mounting element, bringing the face of the ultrasound transducercorrespondingly progressively towards and into operational contact withthe tube wall. Desirably the pivot axis is vertical, e.g. provided on anupright structural element adjacent the column wall. This proposalenables rapid deployment of ultrasound sensing at newly-determinedoperating positions. For best results the axis of the threaded adjusteris preferably perpendicular to the tube wall, i.e. radial relative tothe tube.

Flow Control

Another aspect herein (preferably combined with any one or more or allof the aspects above) is particularly concerned with expanded bed orfluidised bed processes, in which process liquid flows out of the columnthrough a top outlet opening, preferably in a top end cell or toppiston, but optionally in a free outlet conduit end that does not closeoff the column tube interior.

As mentioned above, the maintenance of a stable and effective expandedbed is challenging. One challenge is to avoid the formation of vorticesin the liquid upflow. In the expanded bed apparatus and processesdescribed herein, we prefer to use a process liquid inlet injectionarrangement having an array of process liquid injection holes in adistribution rotor. These rotors have significant advantages, but theirrotation naturally tends to initiate vortex formation in the bed volume.It is known to reverse the rotation direction from time to time toreduce this tendency, but it can still be a problem. Moreover, evenwithout a rotational structure at the process liquid input, liquids havea tendency to form vortices where they flow out from a larger volumethrough a restricted conduit, such as from the bed volume out throughthe process liquid outlet of an expanded bed process.

Noting this, we have found that vortex formation can be usefully reducedby providing a vortex-inhibiting structure beneath the outlet opening,preferably as part of the outlet structure or as part of a piston or endcell structure which incorporates the outlet structure. Thevortex-inhibiting structure comprises one or more divider, partition orslot-defining elements. These may be disposed in the opening and/orprojecting down below the opening entrance, and/or projecting radiallyout beyond it. The one or more elements desirably extend(s)substantially radially, e.g. in radial planes, relative to the outletaxis. This structure divides the flow entering the outlet, and inhibitsrotational movements around the outlet axis.

Preferably it comprises two or more upright radial vanes projectingdownwardly and outwardly relative to the outlet opening, so as to reduceor inhibit rotational flow.

The structure may also comprise a downwardly-facing baffle, desirably ator below the level of the vanes or partitions, to promote approach ofliquid to the outlet in a radially inward rather than axial direction.

Preferably the vortex-inhibiting structure for the outlet isincorporated in a fitting which is attached at or to the underside(inside face) of a movable top piston. Additionally or alternatively itor part of it (e.g. vanes) may be incorporated in the structure of thepiston face. As mentioned, it may also be used in a column with anon-movable end cell, especially top cell, such as in a fixed wall or anon-moving or non-adjustable piston.

A preferred embodiment combines the above vortex inhibitor with afeature of a movable piston which is itself another new and independentproposal herein, namely a piston component or fitting with a lowerextremity or structure which projects down axially below the peripheryof the piston (which desirably has a dished or coned lower surface) toform a bump stop, so that if for any reason the piston should fall downinside the column, this (preferably central) lower extremity meets thestructure at the bottom of the column first. The centre is typically astrong point, e.g. the hub of a rotary process liquid injection rotor,the outer parts of which would be vulnerable to damage if the pistonfell on them. In the preferred embodiment the bump stop extremity andoptionally also the vortex-inhibiting structure themselves are formed ofpolymeric or plastics materials to reduce the impact, and may be formedas a single unit e.g. in one piece. Preferably the extremity isdownwardly convex to avoid trapping e.g. of air.

It is also a proposal herein to provide a vortex-inhibiting structure asdescribed above at the inlet to the operating volume, such as at thebottom of a column tube. The options above are all applicable, but theother way up. Vortex-inhibiting structure may be provided at both ends.

Preferred Embodiments Expanded Bed Adsorption Column

Drawing together the proposals above, preferred embodiments of ourproposals are EBA columns and processes having a movable top piston,pneumatically-operable as discussed above, and preferably with sensormeans for detecting or monitoring one or more positions of piston,liquid, bed front, particles, bed conditions or solute concentrationsetc. as mentioned above, desirably also with feedback or dependency forthe pneumatic actuation to control the piston in dependence on theposition(s) or condition(s) detected by the sensor means. A top plate ofthe column may define the top of the pneumatic gas space. The processfluid exit conduit (piston exit conduit) is a flexible conduit or hosewhich may pass sealingly right through the top plate, or may connect toa fixed union in the top plate which connects the interior flexibleconduit section with an exterior conduit section. One or more actuatinglines, e.g. one or more pneumatic actuating lines, for any of dynamicoperating seal(s) and/or piston tilt-preventing contact structureelements, may also pass sealingly through the top plate, or be connectedthrough it via a fixed union. Since the top plate should make anairtight seal, it is preferred to leave it in place without disturbingits main peripheral seal. It may be for example bolted onto a top flangeof the column tube. In this proposal and in the movable piston proposalsin general it is preferred to provide a removable access hatch in thetop plate so that routine operations such as cleaning (e.g. spraying inliquid) and visual inspection can be done without removing the top platefrom the column tube. Thus, the hatch opening is desirably at least 50mm, more preferably at least 100 mm across, e.g. a circular opening, sothat e.g. a hand can pass through. The removable hatch cover makes afluid-tight seal, desirably sealing out sideways with a sliding (plug)seal against the edge of the hatch opening.

At the bottom of the column, the apparatus preferably has a processliquid injection rotor with an array of injection holes, and a drive torotate it. These are known, and a skilled person can choose a suitableone for the purpose in hand. Usually the bottom of the column is closedoff by a fixed end plate, which may have a separate hole for thedraining and optionally injection of the column contents (mediaparticles). This can be a sanitary valved hole.

The underside of the top piston preferably has an anti-vortex structureas described above, which also preferably includes a lower bump stopextremity which is a lowermost part of the piston, so as to limit impactin case the piston falls.

Desirably the flexible outlet conduit is able to take the weight of thepiston. Optionally a supplementary tether is provided, e.g. a wire whipcheck, that connects between the piston and the top plate to absorbinitial energy should the piston fall, protecting the flexible conduitagainst shock loads. The flexible conduit may be made e.g. ofwire-reinforced polymeric hose.

The column may be mounted on or connected to a mobile platform (“skid”),in a generally known way. A programmed control unit may be provided foroperating the pneumatic drive, and may be integrated into the skid(programmable control platform).

The apparatus preferably comprises a gas filter to clean (sterilise) thegas, typically air, which is pumped into the pneumatic space above thepiston.

Conventional or known media may be used for the EBA, according to theskilled person's knowledge. As is well known, preferred media particlesfor EBA are density-controlled, usually having a high-density core e.g.of quartz, tungsten carbide, zirconia or steel, and an active coat, e.g.of agarose gel, carrying selective binding groups for the targetsubstance, e.g. Protein A for antibodies.

The apparatus and processes herein may be used for the production orpurification of drugs, biopharmaceuticals, hormones, vaccines, ordiagnostic agents, or biologically-produced precursors of these.

BRIEF DESCRIPTION OF THE DRAWINGS

Having described the general concepts proposed, we now describe exampleswith reference to the accompanying drawings in which:

FIG. 1 is an axial cross-section of an EBA column embodying theinvention.

FIG. 2 is a plan view of the column, showing a line A-A for the sectionof FIG. 1.

FIG. 3 is a radial cross-section at B-B of FIG. 1.

FIG. 4 is a radial cross-section showing details of the piston and topcover of the column.

FIG. 5 is an oblique view of the piston separate from the column.

FIGS. 6( a) and 6(b) are oblique schematic views of piston designsshowing conceptual alternatives for tilt-preventing structures.

FIG. 7 is a plan view of a bottom plate with the column tube removed.

FIG. 8 is a fragmentary sectional view through the top cover showingsealed fitting of an air input to an air chamber.

FIG. 9 is a schematic side view of the column indicating an array ofsensors and elements of the column tube contents for EBA to be detectedthereby.

FIG. 10 is a fragmentary sectional view through a segment of tube wallshowing a way of mounting an ultrasonic transceiver.

FIG. 11 is a schematic diagram showing more details of an air supplysystem.

FIG. 12 shows schematically a column of packed-bed type with a movablepiston according to our proposals.

DESCRIPTION OF THE SELECTED EMBODIMENTS

For the purpose of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described embodiments, and any further applications of theprinciples of the invention as described herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates. One embodiment of the invention is shown in great detail,although it will be apparent to those skilled in the relevant art thatsome features that are not relevant to the present invention may not beshown for the sake of clarity.

With reference to FIGS. 1 to 3, an expanded bed adsorption (EBA)apparatus comprises a vertical column tube 1 clamped between a top plateor cover 3 and a bottom plate 4 by a set of tie bars 11. In thisembodiment the column tube 1 is of transparent polymer, e.g. acrylic.The column shown is 300 mm in internal diameter, 25 mm wall thickness.The tube may be e.g. from 1 to 2 m in height.

The bottom plate—see FIG. 7—carries a rotational process fluid inputdevice 41, in the form of a circular rotor with radially-projecting arms43 and a hub 42. Each arm has a series of downwardly-directed holes. Therotor 41 is drivable in rotation by a motor 44, and a process liquidinlet 45 is connected to feed process liquid up into the hub 42 of therotor and along the arms 43, to be injected into the operating volume 13of the column tube at positions distributed across the base plate 4.Rotors of this kind are known to the skilled person, and exist invarious forms. In addition to feeding process liquid for separation,such as a cell broth homogenate, the rotor can be used to feed plainbuffer for establishing a bed, or for washing media out of the columnthrough a slurry inlet/drain hole 46 in the base plate 4. Preferably thedrain hole 46 is also used as an inlet for feeding slurry of mediaparticles into the column, being often preferable to loading the mediafrom the top.

A self-aligning piston 2 operates in the column, dividing it into anoperating volume 13 between the piston and base plate 4 and a pneumaticcontrol space or chamber 77 between the piston 2 and top cover 3. Thepiston 2 consists of a closed circular piston plate 21 connected by anopen upwardly-extending frame (in this case a set of four verticalstruts 85) to a contact ring 81 which constitutes a stabilising ortilt-preventing part of the piston.

In more detail, with reference to FIGS. 4 and 5, the piston body orpiston plate 21 carries a peripheral elastomeric sealing member 23, heldin place by a clamping flange 212. In this embodiment the seal 23, whosefunction is to form a fluid-tight separation between the pneumatic space77 and the operating volume 13, is a dynamic seal which can be energisedwith compressed air, by means of a compressed air line 71 connectingbetween a working space 881 defined inside the hollow seal member 23 viaa connector 871 on the piston body 21. This air line 71 (see FIG. 1)passes in a sealed mode through the cover plate 3 and to a pressurisedair control unit 6, connected in turn to a pressurised air supply 7.These are shown schematically in FIG. 1, and may use per se conventionaltechnology. FIG. 4 shows the piston seal 23 in its non-energisedcondition, in which there is some clearance between seal and tube wallto enable cleaning. Desirably for this purpose the clearance issubstantially larger than the largest diameter particles to be used inthe process, so that particles can be reliably washed away from thesealing faces. When the pressurised air is fed to the seal's workingspace 881, e.g. at excess (gauge) pressure up to 6 bar, the seal isforced out against the column tube wall to make a fluid-tight seal andalso prevent movement of the piston 2 up or down the tube. By reducingor relieving the pressure supply, e.g. to 2-3 barg, sliding of thepiston may be allowed.

The piston 2 is not guided by any axial rod or tube extending outthrough the top of the column, unlike some known constructions. Topreserve its axial alignment, i.e. to stop it from tilting as it moves,it comprises an inbuilt tilt-prevention structure in the form of acontact ring 81 which, by virtue of being axially spaced from theannular locus of the piston seal 23, contacting around the interior ofthe tube, prevents the piston from tilting. The axial spread or span ofthe piston seal and contact engagements (“X” in FIG. 5) is determinedrelative to the piston diameter (“D” in FIG. 5) so as to inhibit tiltingsufficiently that the piston seal remains fully in contact with the tubewall, and hard piston material cannot contact the tube wall.

In this version the stabilising contact ring 81 consists of a rigidsteel support ring 810 carrying an inflatable annular elastomeric sealelement 83, similar in structure and operation to the piston sealitself, which contacts the tube wall. However this contact seal 83 hasno intrinsic sealing function, because the support ring 81 is open; itspurpose is only to make an even and controllable contact around the tubeinterior. This contact can be controlled by the supply of pressurisedgas along a stabiliser contact air line 72 connecting to thecorresponding stabiliser seal working space 882 through a connector 872on the support ring 810. Again, this air line 72 passes in a sealingmanner through the cover plate 3 of the column and to theabove-mentioned air control unit and air supply.

The piston 2 defines the top of the operating volume for the EBAprocess, including an outlet for the process liquid. The piston has aconically-recessed underside converging towards the central outlet. Thisembodiment cone has an angle of about 18°, and this steep angle helpsescape of any air bubbles. At the centre, an outlet flow connector orunion 24 is fixed through a central orifice of the piston plate 21, andhas a top clamp fitting 241 e.g. a triclamp fitting for connection of aflexible outlet hose 9 above the piston. With reference to FIGS. 1 and4, the outlet hose 9 connects at its other end to a fixed connector orunion 33 (triclamp to triclamp through the top plate) communicating in asealing fashion through the cover plate 3 to an external outlet conduit.The outlet hose 9, desirably of wire-reinforced silicone tubing, isflexible to accommodate movement of the piston 2 up and down inside thecolumn tube 1, strong enough to support the weight of the piston, andshort enough to hold the piston off the bottom plate.

On the underside of the outlet connector 24 a vortex-inhibitor device 25is fitted, in this case by screws on a flange which is part of theanti-vortex device, which passes down (FIG. 4) through the piston and isstopped by the flange, having holes for bolts screwing into the pistonbody 21 (stainless steel). The vortex inhibitor in this embodimentcomprises a unit with a set of three flat radial vanes at 120° to oneanother and meeting along the axis. These inhibit rotational flow(vortex formation) as liquid leaves the operating volume 13 through theoutlet and into the conduit 9. This inhibition of rotational flow at theoutlet helps to prevent undesired disruption of the media bed in theregion adjacent the outlet. Additionally, approach to the outlet fromdirectly beneath is blocked by a baffle portion 26 of thevortex-inhibiting fitting 25, so that liquid approaches primarilyradially rather than axially. In this embodiment the baffle portion isextended to form a nose or bump stop 26 which projects axially below thepiston body. The bump stop/vortex-inhibitor fitting is made of a singlepiece of engineering plastics, such as PEEK. Should the piston 2 byaccident be dropped down the column with the sealing rings 23,83released and the hose 9 not in place to stop it, the bump stop 26 willstrike the central hub of the input rotor at the bottom (or other strongcentral structure, according to the design) avoiding damage caused bythe peripheral sealing parts of the piston hitting the bottom plate orrotor.

In this embodiment the top stabilising contact ring 83 can bepressurised in the same way and to the same pressure as the sealing ring23 proper. However this is just one option. It is also possible to useordinary elastomeric seals, without pneumatic actuation. Or, differentmechanisms may be provided, actuated either pneumatically or by othermeans, for urging the seals or contact structures either out against thetube wall, or in away from the tube wall to allow movement of the pistonand/or passage of cleaning liquid. One suitable construction uses aninflatable seal for the piston seal 23 and a simple elastomer ring forthe top contact, so that some frictional restraint is always imposed onmovement of the piston 2.

The illustrated piston is based on a primarily steel structure apartfrom the vortex-controlling outlet, but the skilled person willappreciate that other material types may advantageously be used asdiscussed earlier.

A pneumatic space 77 is defined above the piston, the outlet hose 9 andany energising air lines 71,72 for the piston components extending inisolated fashion through the pneumatic space 77. The pneumatic space 77is connected also to a pressurised air supply via the air chamber airline 73, also connecting to the air supply 7 via the air control unit 6.By adjusting the air pressure supplied to line 73, the pressure in theair chamber 77 can be controlled to move the piston 2 up or down, or tomaintain its position against changing pressures beneath from theup-flowing process liquid in the operating volume 13. In practice wefind that this can readily be achieved with air gauge pressures lessthan 3 bar against seal pressures of 2-3 bar. The air line 73 mayoptionally incorporate an air filter, such as a submicron disposablefilter, enabling the pneumatic space 77 to be kept sterile which is notpossible in previous movable-piston EBA columns.

A circular access hatch 311,312 is provided in the top cover plate 3 sothat routine operations such as cleaning (e.g. spraying in liquid) andvisual inspection can be done without removing the top plate from thecolumn tube. In this embodiment the hatch opening 312 is 100 mm diameterso that a hand can pass through. The removable (bolted) hatch cover 311makes a fluid-tight seal, sealing out sideways with a sealing ringagainst the edge of the hatch opening 312. The construction shown hasthe air hose union 33 offset from the centre to maximise space for thehatch, but depending on overall dimensions it may be preferable to havethe union central.

FIG. 8 shows how the air chamber air line 73 may be connectedfluid-tightly and securely into the cover plate 3, using a swagedconnector of the “Swagelok” type, comprising a main fitting 731 thatscrews into a threaded bore in the plate 3 with a bottom shoulder, ametal-supported seal (“Dowty seal”) beneath the flange of this, and atop swaging nut 732 to clamp the end of the air line 73 by means of anentrapment washer 733 and a tapered wedge washer 734 of soft material toseal against the air line tube 73. The air supply lines 71,72 to thepiston may pass through similar fittings, except that because these airlines pass right through they have an identical sealing clamp on theunderside too.

FIG. 11 shows details of an air supply arrangement. In this arrangementair supply lines 71,72,73 for the top seal, bottom seal and pneumaticchamber are taken from a main supply line 700 e.g. from a 7 bar aircylinder. Each of the individual supply lines has, in sequence, aprecision air regulator 705, a unidirectional valve 706 (e.g. a ballvalve) to prevent back flow, a relief valve 708 for venting air in caseof excessive pressurisation, and a pressure gauge 707. The regulator 705for the pneumatic chamber line 73 provides for a smaller pressure rangeup to 4 bar whereas the inflatable seal lines 71,72 regulate up to 7bar. The pneumatic chamber pressure acts on the outsides of the seals,so they need to be able to be pressurised to a higher pressure toguarantee the necessary outward mechanical force again the column wall.

It will be understood that the stabilising function of the top ring 81seen in FIG. 5 does not intrinsically require a seal. A variety ofalternative structures may be used to provide adequate tilt-prevention,therefore. Some such structures are illustrated schematically in FIGS.6( a) and 6(b). FIG. 6( a) shows a tilt-preventing structure supportedthrough a frame as in the previous embodiment, but having a contact ring8′ which contacts the column tube interior intermittently atcircumferentially-spaced positions, through a plurality of projectingslider contact portions. These might be of hard plastics. In FIG. 6( b),a similar effect is achieved by vertical fins 8″ distributed around thetop of the piston 2, and projecting high enough to stabilise it againsttilting. The skilled person will readily conceive other possibilities,depending on the dimensions of the column, the type of piston seal andthe materials to be used.

FIG. 1 shows the air control unit 6 only schematically. Generally itcomprises for each air line 71,72,73 a respective shut-off valve,enabling the air chamber or seal components to be isolated while in apressurised state, or opened to the pressure supply or to vent. It alsoincorporates respective pressure gauges to monitor the line pressures.It may have a manual-precision air regulator control for adjusting theindividual line pressures. Most preferably it also provides forautomated control in dependence on certain sensed conditions in thecolumn tube, as indicated schematically in FIG. 1 by reference numeral 5to indicate inputs from sensors which monitor conditions in the columnat various positions.

To illustrate the possible roles and operation of sensors, see FIG. 9which shows schematically the contents of the column tube 1. The piston2 is shown at a primary position, also at alternative positions 2′ and2″. FIG. 9 also shows characteristic conditions in the operating volume13 during expanded bed operation, namely a bed region 14 consisting ofthe dense media particles, a top “headspace” of clear liquid immediatelybeneath the piston 2, and a turbid band or layer 15 between theheadspace 16 and bed proper 14. This turbid layer contains fines fromthe mass of media. It is desirable to run the process with anappreciable headspace so that fines are not washed out of the operatingvolume 13 through the outlet. FIG. 9 also shows an array of six sensors5, here numbered as 1 to 6, distributed down the wall of the column tube1. These are desirably ultrasonic transceivers, which emit into the tubeinterior and detect characteristic echoes which differ according towhether they encounter empty space, the presence of the solid piston,headspace liquid, expanded bed 14, fine particles in the turbid region15, raised solute concentration etc. The deployment of ultrasonictransceivers on vessels of this kind, and control circuitry for them,are known in themselves. However in this apparatus they are used in adistinctive way to facilitate control—either manual or automated—of thepiston position, by means of adjusting the pressure in the pneumatic airspace 77.

The skilled person will be able to conceive various modes in which thesensors can be used to control the piston position to achieve suitableEBA operating conditions.

In one possibility (“Aspect A”) the sensors monitor the elements of thecolumn bed. For example Sensor 1 monitors the headspace, Sensor 2 ispositioned to align with the turbid band 15 in the correct operationalposition, Sensors 3 and 4 are to monitor the boundary between the turbidband 15 and the EBA bed proper 14, and Sensors 5 and 6 operate when thebed is allowed to settle (e.g. for elution of product), to monitor thetop of the bed.

Another possible operational mode (“Aspect B”) is as follows.

Sensors 1 and 2 define between them a range of appropriate positions forthe piston 2. Initially, a piston may be positioned somewhat above theintended piston height during operation in expanded bed mode. Liquid onthe column side, e.g. plain buffer, is flowed upwards to fill the linesand fill the column. By closing off a valve in the outlet conduit abovethe connector 33 (not shown) liquid pressure will rise in the operatingvolume 13 and push the piston up, starting to compress air in the airchamber 77. When the piston 2 reaches Sensor 2, Sensor 2 sends a signaland the air control unit 6 responds by initialising a routine to stopfurther piston movement, by e.g. pressurising the inflatable seals 23,83to stop the piston, by opening the process liquid valve to allow processliquid to flow out again, by increasing air supply into the top chamber77 to give the desired pressure differential between the air above andthe liquid below the piston, or by some combination of these steps. Thiscan maintain the piston in the desired operating height zone withoutpassing Sensor 1 (which, if actuated, indicates a problem and mayautomatically trigger a halt in process liquid flow).

In Aspect B, Sensors 3 and 4 can monitor the position of the interfacebetween the clear supernatant 16 and the turbid zone 15, to ensure thatthe fines in the turbid zone do not leave the column and foul downstreamequipment. In combination with the pressurised air control unit 6 andsuitable operating software or program control, they can prevent thepiston being pushed down into the turbid region. Sensors 5 and 6 canindicate a position for the top of the particle bed 14 and definedesired tolerances for the bed height: if Sensor 6 detects the boundary,the air chamber pressure can be dropped or the liquid pressure increasedto move the piston up. It stops when Sensor 5 detects the boundary.Conversely, if the piston were too high, Sensor 5 would fire and theopposite routine would operate. The piston can then be maintainedbetween Sensors 5 and 6.

A further possibility (“Aspect C”) is to operate with three sensorsabove the piston (or the interface between the turbid zone and the clearheadspace) and three below. In relation to the selected element (pistonor interface) the three sensors in each direction could indicate degreesof deviation from a target position, e.g. Sensors 3 and 4 indicatingrespectively the upper and lower boundaries of the desired positionband, Sensor 2 indicating “high” and Sensor 1 indicating “very high”.Similarly for “low” and “very low” positions with Sensors 5 and 6. Thecontrol unit 6 can be programmed to initiate, for each detected position(fired sensor) an appropriate routine of events such as opening andclosing valves, operating pumps, increasing or decreasing air pressureand the like to adjust the conditions on the column so the piston (orinterface) remained in the target area.

Finally, we show a way of mounting an ultrasonic transceiver 51 so thatit can conveniently be brought into good operating contact with thesurface of the tube wall 1. See FIG. 10. A horizontal elongate mountingmember 52 is clamped so that it can pivot around one of the upright tiebars 11. The ultrasonic transceiver 51 is mounted at one end of themounting member 52. At the other end a threaded adjuster 53 is provided,aligned substantially radially with the column tube. Desirably theadjuster 53 is of plastics material, so as not to scratch the tube.Clamping screws are provided (not shown) so that the transceivermounting 52 can be positioned and held at any desired position up ordown the tie bar 11. Further sensors may be positioned on the same orother tie bars. A visual length scale may be provided as well, tofacilitate positioning. When the threaded fastener 53 is tightenedthrough the corresponding threaded hole in the mounting member 52, by alever effect the face of the transceiver 51 is brought gradually intocontact with the outside surface of the tube wall 1. By this means thetransceivers can easily be brought into an appropriate pressure contactagainst the tube surface, which is important for effective operation.The transceiver device likewise is then radially-oriented relative tothe tube.

FIG. 12 shows schematically the application of the present “balancedpiston” concept in a packed bed column, in which the bottom end cell 104(which may be a conventional packed-column design) and the top end cellincorporated in the present piston 102 are provided with media-retainingmesh layers 1041,1021 mounted over per se conventional convergentcollection surfaces leading to and from process liquid conduits1042,1022. To obviate the conventional support rods projecting up out ofthe top of the column in a conventional column, a top piston 102embodying the present proposals is used and comprises a stabiliser ring181 carrying a peripheral contact member 183 (formed here as a rubberseal ring, although without sealing function) spaced by an open frame185 above the main piston seal to prevent it from tilting. A top coverplate 103 defines a pneumatic space 177 above the piston 102 to receivepressurised air or other gas via gas supply 173. An array of ultrasoundsensors 151 is provided up the wall 101 of the column. These are usefulto control the processes and/or the movement of the piston 102. They maybe used to control the piston movement on detecting the correctposition, or other parameters in the bed. If inflatable seals are used,as in the earlier embodiment, additional air inlets to supply these maybe provided through the cover plate 103. In this embodiment a steelcolumn wall 101 is envisaged. The column may be e.g. about 2 m indiameter.

Packing of the column and chromatographic processing may be byconventional methods. Slurry may be injected into the column bed space113 through a central multi-functional packing valve of known type, orthrough a simple valve with slurry lines, communicating through the baseand mesh as indicated at 146. The bed can then be packed by driving thepiston down and this may be by pneumatic pressure rather than theconventional mechanical or hydraulic drives

The present balanced piston in a packed bed column can avoid thepresence of moving parts and complex mechanisms such as hydraulic orpneumatic drives extending above the envelope of the column. Beingrelatively mobile under controllable conditions, the top piston mayeasily be position-adjusted during use, e.g. to accommodate the swellingor shrinking of a packed bed according to changes in the ionic strengthor nature of the buffer or other process liquid in which it is immersed.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges, equivalents, and modifications that come within the spirit ofthe inventions defined by following claims are desired to be protected.All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference as if each individualpublication, patent, or patent application were specifically andindividually indicated to be incorporated by reference and set forth inits entirety herein.

1. A chromatography apparatus comprising: a column tube having a tubeaxis defining an axial direction of the apparatus; first and second endcells which close off the column tube, defining between them anoperating volume in the column tube; at least one of the end cells is amovable piston, slidably movable inside the column tube in the axialdirection thereof and comprising a peripheral operating seal to sealagainst the inside of the column tube; said movable piston comprising apiston body comprising the operating seal; and a tilt-preventionstructure projecting axially from the piston body and connected to berigidly axially aligned therewith, wherein the tilt-prevention structurecomprising a circumferentially-distributed contact structure whichengages around the interior of the column tube at an axial spacing fromthe operating seal.
 2. The chromatography apparatus of claim 1 in whichsaid movable piston is free of rigid structure passing through any fixedcolumn end structure of the apparatus.
 3. The chromatography apparatusof claim 1 in which said contact structure is annular and engagescontinuously around the column tube interior.
 4. The chromatographyapparatus of claim 1 in which the contact structure is radially movablerelative to the tilt-prevention structure; and the movable pistoncomprises a contact structure actuating mechanism operable to urge thecontact structure radially outwardly against the column tube interiorand/or to retract it to a radially retracted condition or position. 5.The chromatography apparatus of claim 1 comprising an outer closure ofthe column tube, and in which the movable piston, column tube and outerclosure define a pneumatic space outside the movable piston, separatedfrom the operating column, and a pressured gas supply for supplyingpressurised gas into the pneumatic space to act on the movable piston.6. The chromatography apparatus of claim 1 in which the contactstructure comprises an elastomeric ring.
 7. The chromatography apparatusof claim 1 in which the engagement of the contact structure with thecolumn tube interior is around a single annulus at a constant axialspacing from the operating seal.
 8. The chromatography apparatus ofclaim 1 in which the tilt-prevention structure is an open structurecomprising any of rods, legs and struts with intervening spacing.
 9. Thechromatography apparatus of claim 1 in which an axial extent of thecontact structure, said axial extent being the maximum axial distancereached by the contact structure from the axial position of theoperating seal, is at least 25% of a diameter of the movable piston. 10.The chromatography apparatus of claim 1 in which the operating sealcomprises an elastomer ring in a peripheral channel of a piston body.11. The chromatography apparatus of claim 1 comprising a pneumaticmechanism for the radial advance or retraction of the operating seal.12. The chromatography apparatus of claim 1 comprising sensors to detectthe axial position of the movable piston in the column tube.
 13. Thechromatography apparatus of claim 1 in which the movable piston has acentral process fluid outlet and comprises a vortex-inhibiting structureat said process fluid outlet, the vortex-inhibiting structure comprisingone or more divider, partition or slot-defining elements.
 14. Achromatography apparatus comprising: a column tube having an insidesurface and a tube axis defining an axial direction of the apparatus; amovable piston, slidably movable inside the column tube in the axialdirection and comprising a peripheral operating seal to seal against theinside surface of the column tube; said movable piston having a diameterand comprising a piston comprising the peripheral operating seal; atilt-prevention structure projecting axially from the piston body, thetilt-prevention structure comprising an annular contact structure whichengages around the inside surface of the column tube at an axial spacingfrom the operating seal which is at least 25 percent of the diameter ofthe movable piston; and an open frame structure connecting the annularcontact structure rigidly to the piston body.
 15. The chromatographyapparatus of claim 14 in which the movable piston has a central processfluid outlet.
 16. The chromatography apparatus of claim 14 comprising apneumatically-actuated mechanism to urge the contact structure radiallyoutwardly against the inside surface of the column tube.
 17. Thechromatography apparatus of claim 14 in which the contact structurecomprises a polymeric ring to contact the inside surface of the columntube.
 18. A chromatography apparatus comprising: a column tube having atube axis defining an axial direction of the apparatus; a fixed outerend closure of the column tube; an end cell comprising a piston slidablymovable inside the column tube in the axial direction thereof andcomprising a peripheral operating seal to seal against the inside of thecolumn tube, said movable piston being free of rigid structure passingthrough the fixed outer end closure, and whereby the movable piston,column, tube and outer end closure define a pneumatic space in thecolumn tube; and a pressurised gas supply inlet for the supply ofpressurised gas into the pneumatic space to act on the movable piston.19. The chromatography apparatus of claim 18 in which the movable pistonhas a process fluid outlet, a sealed connector is provided extendingthrough the column tube or through said outer end closure, and aflexible conduit is connected at one end to the process fluid outlet andat the other end to the sealed connector.
 20. The chromatographyapparatus of claim 18 in which the operating seal comprises an elastomerring and the apparatus comprises a pneumatic mechanism operable toadvance or retract the operating seal radially relative to the piston,so as either to urge the operating seal outwardly against the inside ofthe column tube or to retract it to a radially retracted condition. 21.A chromatography process carried out with the chromatography apparatusof claim 1, the process comprising: providing a bed of particulatemedium in the operating volume; adjusting the position of the movablepiston in the axial direction towards the bed of particulate medium; andpassing a process fluid through the bed of particulate medium.